Stallion’s voice: an indicator of fertility and a basis for female choice? (#5)
Vocalisations of mammals, carrying information on caller’s familiarity, identity, age or size, play a key role in coordinating sexual partners. Some studies showed that females select partners based on vocal attributes. However, we still fail to understand why such capacities evolved and which consequences these choices can have on reproduction. Wild mares actively choose the family group into which they are going to migrate, spotting at a distance the potential stallion partners. Whinnies are vocalizations allowing long-distance communication and we thus investigated if and how they could guide the choice of females. At first, the voices of 15 reproductive stallions were recorded in three national Stud farms while they were held at a distance from a mare. Acoustic analysis then showed that there was a correlation between frequency parameters and the reproductive success of the caller, stallions with a higher-pitched voice presented more successful gestations. Interestingly, acoustic parameters appeared to be more reliable predictors of fertility than seminal and hormonal features. Secondly, 40 adult mares were individually exposed to the simultaneous loud-speaker playback of pairs of whinnies (high- and low-pitched). Mares showed a very clear preference of orientation towards low-pitched voices. These results open lines of basic and applied research on the relationship between vocal characteristics and reproduction in mammals.